SOCIAL ORGANIZATION WITHIN CLONES OF THE SEA ANEMONE ANTHOPLEURA ELEGANTISSIMA

The aggregating form of the anemone Anthopleura elegantissima often lives in closely packed groups composed of genetically identical individuals. These clonal aggregations remain separated from each other because contact between non-clonemates elicits intraspecific aggression (Francis, 1973a & b). Since the anemones live in a dependable environment, are long-lived, have indeterminate growth, and reproduce sexually and asexually, and since predation does not appear to be severe, intraspecific competition for space is quite important. The ability to distinguish clonemates from non-clonemates allows the anemones to benefit from group living while interfering with all other conspecific competitors. A high proportion of the costs of this intraspecific aggression is paid by the anemones living at interclonal borders. The interclonal border warriors have more and larger acrorhagi (specialized structures used in intraspecific aggression) than clonemates elsewhere in the aggregation and were without gonads in June when many of their clonemates were ripe. They are smaller on an average than midclone anemones but not smaller than clonemates from an edge of the aggregation remote from other clones. In the field, the fission rates of warrior anemones is not higher, and may be lower than that of clonemates in other parts of the same aggregation. Lack of gonads, small size, and low fission rates probably indicate that the warriors have less energy available for growth and reproduction than do their clonemates away from the battle zone. Without physical connections among the individuals, the ability to coordinate and communicate is limited. Each anemone responds to its particular circumstances, and in so doing may fortuitously benefit its clonemates. Natural selection acts on the genotype (the clone). This is a very simple form of social organization both functionally and evolutionarily.